A serological and parasitological survey on dogs was done in 4 slum areas on the outskirts of Lisbon and a rural area west of Setubal. The serological test was the IFAT [immunofluorescent antibody test]. The total number of dogs examined was 572 of which 55 (9.6%) had titer .gtoreq. 1/128, 10 of these dogs were among 182 (5.5%) in the urban areas and 45 were in the sample of 320 dogs (11.5%) in the rural area. Dogs (23) with titers of .gtoreq. 1/128 were examned parasitologically. Methods of study included: the examination of tissue from popliteal lymph nodes (by direct examination and by the inoculation of NNN cultures and hamsters), the direct examination of stained smears from sores and the direct examination of stained smears of healthy skin. Parasites were demonstrated in 15 (65.2%) of the 23 dogs; 14 dogs with high titers were followed up by a 2nd IFAT, in which 5 had become higher, 5 had remained the same and, in 4, the titers had fallen. Canine leishmaniasis may be more common in the rural area than in the urban sites. The disease in man in the focus studied appears to be accidental and, paradoxically likely to be acquired rather in the town than in the villages. The reason is probably related to zoophilic preferences of vectors, and is widely dispersed populations in rural areas.